The present invention relates to an independent optical ferrule and optical fiber connector which uses the independent ferrule. The present invention further relates to a replaceable optical plug which uses such ferrule. The "optical ferrule" referred herein implies a member which embeds therein a single or a plurality of optical fibers and position such fiber or fibers in fixed state. The present invention also relates to a method for using such replaceable optical plug for the connection between optical fiber ends or for the connection between the optical fiber end and an light input portion of an optical system or equipment.
FIG. 1(a) shows a conventional optical fiber connector serving as a plug in which single optical fiber connection is attained. In FIG. 1(a), the connector is provided with a ferrule 2 which is produced with high production accuracy to which one end of a coated optical fiber 8 is connected. FIG. 1(b) shows an adaptor housing 9 having a sleeve 10 which functions to align the ferrule of the plug with the axis of another ferrule having the identical configuration of the plug ferrule, when the plugs are inserted into the adaptor housing 9 to provide surface contact between the ends of the two ferrules 2 and 2. The sleeves is adapted to maintain this axial alignment and hold these ferrules in a fixed position.
In FIG. 1(a), a terminal or end ferrule 2 is secured in a plug housing. A coating layer of a coated optical fiber 8 is removed at the end portion thereof to provide a bare optical fiber. The bare fiber is joined to one end of the end ferrule 2 in such a manner that the end face of the bare optical fiber is in alignment with the end face of one end of the ferrule 2. The end ferrule 2 is secured in an internal space of the housing defined by the combination of a push ring member 3 and an insertion guide 5 upon their assembly, and is normally urged by a spring 7 abutting a collar portion S of the terminal ferrule 2.
The insertion guide 5 is formed with a bore in which the terminal ferrule 2 is disposed. Annular stop member 41 is provided in the bore to which the collar portion S abuts. The coated optical fiber 8 extends through a hole of the push ring member 3, while the other end portion of the terminal ferrule extends through the bore of the insertion guide 5 and projects from the open end of the guide 5. The ferrule is normally held in position receiving the biasing force of the spring 7.
The optical fiber connector thus constructed is connected to one end of the sleeve 10 of the adaptor housing 9 and another identical optical fiber connector is connected to the other end of the sleeve 10, so that two connectors confront each other to thus provide an optical connection. A lock nut 6 loosely disposed around the insertion guide 5 is then threadingly engaged with a thread 42 formed on an outer peripheral surface of the adaptor housing 9. As a result, an optical connection line is finally provided.
There is however, a problem such that damage of the end surface of the terminal ferrule 2 causes a loss in optical coupling. Therefore, protection of the end surface of the end ferrule 2 is one of the most important technical problems in the optical fiber connector. To solve this problem, there has been proposed a method of polishing the end surface of the bare glass fiber embedded in the end ferrule 2 in a concave shape. Alternatively, there has been another proposal to provide coating at the end surface of the ferrule 2. In any of these methods, however, it is impossible to completely avoid the damage of the end surface of the ferrule, if connecting and removal operations are repeatedly and frequently conducted. Particularly, if the connectors are coupled to each other through the adaptor together with foreign materials or the like between the ferrule ends, the end surfaces are severely injured.
In spite of the fact that the end surface of the optical fiber connector is such an important part that may determine the optical coupling property, the end surface could not be protected sufficiently, due to the necessity of connecting and removing operations of the connector. In reality, in case the end surface of the terminal ferrule is injured, the damaged portion is cut off after disassembly of the plug, and then reassemble the same. In this case, it takes much time for such disassembly and assembly work of the terminal ferrule as well as connector housing. For example, it takes not less than 20 to 30 minutes for the entire process, such as joining the optical fiber with terminal ferrule end, polishing the end of the ferrule, i.e., the end of the optical fiber embedded in the ferrule, assembling the optical fiber connector, etc. Moreover, setting aside the case where the work is carried out indoors in a good surrounding, it is very difficult to carry out the work outdoors in the surroundings where operators suffer from severe wind and rain. Further, according to the above mentioned ferrule reattaching work, the ferrule is reused. However, if the ferrule end is damaged too much, the ferrule should be cut off at the portion joining with the external optical fiber. In this case, there occurs a further problem that the length of the optical fiber becomes correspondingly short, and the reattaching of the ferrule per se might become impossible due to the shortage of the length of the optical fiber. For example, if the optical fiber is installed inside of a wall of a building, there is no spare length if a new terminal ferrule is joined to the optical fiber, since several lengths of the optical fiber is consumed by the cutting and rejoining work.